When Iowa and Iowa State started coming to the Dome in the late 80's, there were probably almost as many Hawkeye and Cyclone fans as Panther fans in the stands. Those early games were novalty games, billed to set attendance records.
View of the Jan. 3,1990 Iowa @ UNI game. Attendance: 22,676, UNI won 77-74
http://wcfcourier.com/image_3d7f2b90-71 ... 25c2d.html
Over time, interest faded but there were still large contingents of visiting fans. Then Iowa and Iowa State started getting bad, UNI started getting good, and now it's mostly UNI fans.